This invention relates to the monitoring of pipelines or other conduits to determine the nature of desired characteristics of the pipeline, such as the magnitude and/or gradient of stresses on the pipeline and the time rate at which they develop. The invention further relates to the detection of potential or actual failure places in a pipeline.
Pipelines are widely used for transporting all types of fluid materials such as oil, liquid chemicals, slurries, particulate matter, natural and other gases, etc. There have recently been installed extremely long pipelines for transporting oil across vast distances, such as the Alaskan pipeline, and pipelines for transporting natural gas across similar distances are soon to be constructed. In some situations, especially with regard to the transport of such natural resources as oil and natural gas to distant locations such as distribution points, the pipeline must pass through barren regions having harsh natural environments where temperatures are likely to be extremely low and to vary greatly. For example, pipelines passing through the frigid regions of Alaska, Northern Canada and Siberia are expected to encounter alternate freezing and thawing conditions which cause movement of the earth on or in which the pipeline is situated. Not only can varying weather conditions cause such freezing and thawing, but the preheating of material in the pipe to improve its flow can cause localized thawing in an otherwise frozen environment. Similarly, gas at a temperature below the freezing point of water can cause the freezing of an otherwise unfrozen environment. Even if the pipeline is mounted on supports above the ground or on a gravel bed beneath the ground, unstable soil conditions resulting from such freezing and thawing can cause the pipe to heave and impose substantial pressures on the pipe. If these pressures, in combination with those due to the fluid in the pipe, exceed the critical limits of the pipe, rupture may occur. In view of the high flow rate of the material through such pipelines, and in further view of the liklihood that a rupture would occur in a remote region, the economic losses and environmental damage from such a rupture could be severe. The need for some means of avoiding pipeline ruptures is thus very great.
There has heretofore been no means devised for satisfactorily monitoring gas or other pipelines to warning of impending rupture or other failure. There have been suggestions to employ radar detection, satellite detection and inertial guidance techniques for performing the monitoring function. However, these techniques all involve indirect monitoring because there is no physical interface with the pipe structure, and are therefore inherently deficient. Moreover, none are known to have been successfully employed. What is preferred, and what the present invention provides, is a direct monitoring system, where stress measurements are taken directly through a physical contact with the pipe.